Compositions, to be suitable as decorative or protective coatings, should provide coatings having good adhesion characteristics in the presence of water and/or organic solvents. In order to provide such adhesion, the cured coating needs to be resistant to both solvation and swelling when in contact with such solvents. On the other hand, the cured coating needs to be easily removable when it is desired to change the decorative coating or place the protected component into use.
One way to remove a decorative or protective coating is to treat it with a solvent for the coating material. The solvated coating then becomes fluid and can be wiped off as a paste-like material. However, this removal technique can be quite messy. For example, when fingernail polish is treated with the usual polish remover, the solvated coating becomes a fluid mass that must be wiped off with an absorbent material. Wiping away this fluid mass, which usually contains color pigments, is very often messy and may leave portions of the solvated coating smeared over adjacent surfaces and lodged in finger or toe crevices. The solvated coating can also be accidentally transferred to other surfaces, such as an article of clothing, from which it may be quite difficult to remove.
Some of the coating compositions of the prior art can be brushed or sprayed onto a surface and upon drying, form a film that can be removed by peeling the film from the surface. Such films have relative poor adhesion characteristics because they rely on removal by a mechanical peeling step alone. Thus, easily peelable films in the past have had the disadvantage of being relatively easily detached by moisture and/or by organic solvents so that they tend to come loose prematurely from the surface of a substrate. Such films may also come loose from the substrate because they do not adhere well to certain materials, such as plastics or other resins or painted surfaces, or because they are actually attacked by the material of the substrate itself. In other words, mechanically peelable coatings are often held on the substrate surface by relatively low levels of interfacial forces. It is therefore desirable that coatings removable as strippable films be easily separated from the substrate surface when desired but otherwise be strongly adhered to the substrate surface by high levels of interfacial forces.
Strippable films are also useful for stenciling the surface of a substrate such as wood, metal or plastic or the painted surface of such a substrate. In stenciling, the substrate surface is sprayed with a coating composition that is dried to form a strippable film coating and the pattern desired is cut in this film coating. The unwanted portions of the film are then stripped from the substrate surface to the leave the stencil pattern behind. The stripped portions of the substrate surface are then coated with ink or a suitable paint. After the ink or paint has dried in the desired pattern, the remainder of the strippable film is removed, leaving the desired pattern on the substrate surface. The advantage of a peelable stencil coating is that contamination or smearing of the dried ink or paint by a solvated coating is avoided.
It would therefore be highly desirable for a strippable coating film to adhere to the surface of the substrate with a high level of interfacial forces during the time that decoration and/or protection is desired, and with a low level of interfacial forces when the substrate surface is to be exposed by stripping off the strippable coating. It is also highly desirable that the coating be removable as a single piece of cohesive film. Furthermore, during removal none of the materials in the film, such as color pigments, should exude or bleed out of the film because such released materials could smear to adjacent surfaces and could be transferred to still other surfaces, thereby creating a mess. It is also desirable that such materials not exude or bleed out of the composition while it is in use for the same reasons. In addition, loss of such materials could change the color or other characteristics of the adhered film.
Accordingly, it is readily apparent that a coating composition, to be suitable for the above purposes, must possess a number of critical properties and characteristics which are quite difficult to achieve. This problem is made more acute when an object also is to formulate a strippable coating composition at relatively low cost.